Slide gates are used to control fluid flow through a passageway or channel. More particularly, and looking now at FIGS. 1 and 2, there is shown an exemplary slide gate 5. Slide gate 5 generally comprises a frame assembly 10 which defines an opening 15 through which fluid flows; a slide plate 20 movably mounted to frame assembly 10 for vertical movement relative thereto so as to selectively open and close opening 15 in frame assembly 10; sealing members 25 for providing a substantially watertight seal between slide plate 20 and frame assembly 10; and an operating mechanism 30 for vertically moving slide plate 20 between its open and closed positions so as to regulate fluid flow through opening 15 in frame assembly 10. As is well known in the art, frame assembly 10 of slide gate 5 is disposed across a fluid passageway or channel 32 so that slide gate 5 can control fluid flow through the fluid passageway or channel 32.
As seen in FIGS. 1 and 2, operating mechanism 30 for vertically moving slide plate 20 within frame assembly 10 generally comprises an elongated screw 35 (sometimes hereinafter referred to as a threaded operating stem) which is secured to the top of slide plate 20 and which extends through a threaded operating nut 40 which is rotatably mounted to the top of frame assembly 10. Rotation of threaded operating nut 40 (e.g., by hand wheel, crank, electric motor, etc.) causes longitudinal movement of threaded operating stem 35 relative to threaded operating nut 40 (and hence relative to frame assembly 10), so as to raise or lower slide plate 20, whereby to open or close the slide gate.
Unfortunately, it has been found that, where the gate operating loads are high (e.g., due to heavy gate weights, substantial frictional forces generated during gate movement, particularly due to water pressure on the gate, etc.), the threads on threaded operating stem 35 and threaded operating nut 40 wear over time. This is particularly true with respect to the threads on threaded operating nut 40, since they are substantially continuously in use (whereas only a portion of the threads on threaded operating stem 35 are in use at any given time). In some cases, such wear can cause the threads on threaded operating nut 40 to fail completely, so that slide plate 20 falls within frame assembly 10 and—unintentionally—closes the slide gate. In this situation, because the threads on threaded operating nut 40 have failed, it is then also impossible to re-open the slide gate using the aforementioned operating mechanism 30. Flooding can result upstream of the slide gate.
The present invention is intended to provide a slide gate with a fall-protection feature, so that thread failure on the threaded operating nut does not result in unintentional gate closure.